Image intensifier devices multiply the amount of incident light they receive and provide an increase in light output, which can be supplied either to a camera or directly to the eyes of a viewer. Image intensifiers are constructed for a variety of applications and hence vary in both shape and size. These devices are particularly useful for providing images from dark regions and have both industrial and military applications. For example, image intensifiers are used in night vision goggles for enhancing the night vision of aviators and other military personnel performing covert operations. They are employed in security cameras and in medical instruments to help alleviate conditions such as retinitis pigmentosis (night blindness).
Image intensifiers include active elements, support elements and supply elements. The active elements include the photo-cathode (commonly called simply “cathode”), microchannel plate (MCP), fiber optic screen (screen), and getter. The cathode detects a light image and changes the light image into an electron image. The MCP amplifies the electron image and the screen changes the electron image back to a light image. The getter absorbs gas which is generated during operation of the tube.
The support elements comprise the mechanical elements which physically support the active elements of the tube. In a standard tube these support elements are the vacuum envelope (known as the body), input faceplate (sometimes also called “cathode”), and the output faceplate or fiber-optic (also called “screen”).
The supply elements in the tube include the chrome contact that is deposited on the faceplate to the cathode, the screen aluminum contact which is deposited on the fiber optic or output faceplate, and the metalizing on the MCP glass. In addition the metal parts in the body assembly also provide electrical contact.
The fiber optics direct the image generated by the screen to a convenient position so that the system optics can properly direct the image to the ocular plane.
Three major components of image intensifier tubes are the photocathode, fiber optic screen (anode), and MCP disposed between the photocathode and anode. These three components are positioned within the evacuated housing or vacuum envelope, thereby permitting electrons to flow from the photocathode through the MCP and to the anode. In order for the image intensifier tube to operate, the photocathode and anode are normally coupled to an electric source whereby the anode is maintained at a higher positive potential than the photocathode. Similarly, the MCP is biased and operates to increase the density of the electron emission set forth by the photocathode. Furthermore, since the photocathode, MCP and anode are all held at different electrical potentials, all three components are electrically isolated from one another when retained with the vacuum housing.
Power is provided to the photocathode, MCP and anode by a high voltage power supply, often in the form of an annulus. The power supply is usually axially aligned to surround the image tube.
It is desirable to display an indication of “low battery” and/or an indication of “IR illuminator ON” to a user of a night vision device. This may be done by use of a low brightness light placed on the exterior of the night vision device to alert the user of the status of the power supply and/or other components. An LED may also be mounted at a convenient location on the exterior housing surface of the night vision device.
Use of an indicator light on the outside surface of the night vision device, however, has shortcomings. In order to view the indicator light, the user must look away from the field-of-view of the eyepiece, and look at the indicator light. After looking at the indicator light, the user may then resume viewing the field-of-view through the eyepiece, but likely only after a time consuming eye-focusing adjustment. In addition, an indicator light mounted on the exterior surface of the night vision device may potentially give away the user's position.
There exists a need for an improved approach to visually informing the user of the status of his night vision device. The present invention addresses such need.